#region Copyright & License

//
// Copyright 2001-2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#endregion

using log4net.Core;

namespace log4net.Filter {
  /// <summary>
  /// Implement this interface to provide customized logging event filtering
  /// </summary>
  /// <remarks>
  /// <para>
  /// Users should implement this interface to implement customized logging
  /// event filtering. Note that <see cref="log4net.Repository.Hierarchy.Logger"/> and 
  /// <see cref="log4net.Appender.AppenderSkeleton"/>, the parent class of all standard
  /// appenders, have built-in filtering rules. It is suggested that you
  /// first use and understand the built-in rules before rushing to write
  /// your own custom filters.
  /// </para>
  /// <para>
  /// This abstract class assumes and also imposes that filters be
  /// organized in a linear chain. The <see cref="Decide"/>
  /// method of each filter is called sequentially, in the order of their 
  /// addition to the chain.
  /// </para>
  /// <para>
  /// The <see cref="Decide"/> method must return one
  /// of the integer constants <see cref="FilterDecision.Deny"/>, 
  /// <see cref="FilterDecision.Neutral"/> or <see cref="FilterDecision.Accept"/>.
  /// </para>
  /// <para>
  /// If the value <see cref="FilterDecision.Deny"/> is returned, then the log event is dropped 
  /// immediately without consulting with the remaining filters.
  /// </para>
  /// <para>
  /// If the value <see cref="FilterDecision.Neutral"/> is returned, then the next filter
  /// in the chain is consulted. If there are no more filters in the
  /// chain, then the log event is logged. Thus, in the presence of no
  /// filters, the default behavior is to log all logging events.
  /// </para>
  /// <para>
  /// If the value <see cref="FilterDecision.Accept"/> is returned, then the log
  /// event is logged without consulting the remaining filters.
  /// </para>
  /// <para>
  /// The philosophy of log4net filters is largely inspired from the
  /// Linux ipchains.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  public interface IFilter : IOptionHandler {
    /// <summary>
    /// Property to get and set the next filter
    /// </summary>
    /// <value>
    /// The next filter in the chain
    /// </value>
    /// <remarks>
    /// <para>
    /// Filters are typically composed into chains. This property allows the next filter in 
    /// the chain to be accessed.
    /// </para>
    /// </remarks>
    IFilter Next { get; set; }

    /// <summary>
    /// Decide if the logging event should be logged through an appender.
    /// </summary>
    /// <param name="loggingEvent">The LoggingEvent to decide upon</param>
    /// <returns>The decision of the filter</returns>
    /// <remarks>
    /// <para>
    /// If the decision is <see cref="FilterDecision.Deny"/>, then the event will be
    /// dropped. If the decision is <see cref="FilterDecision.Neutral"/>, then the next
    /// filter, if any, will be invoked. If the decision is <see cref="FilterDecision.Accept"/> then
    /// the event will be logged without consulting with other filters in
    /// the chain.
    /// </para>
    /// </remarks>
    FilterDecision Decide(LoggingEvent loggingEvent);
  }
}